Support structure of motor-driven steering assist apparatus

ABSTRACT

In a support structure of a motor-driven steering assist apparatus interposed between an upper steering shaft in a steering wheel side and a lower steering shaft in a tire wheel side, a steering angle regulating means for limiting a maximum steering angle of the upper steering shaft is provided between the upper steering shaft and a vehicle body side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a support structure of a motor-drivensteering assist apparatus.

2. Description of the Invention

In a rough road traveling vehicle such as a buggy vehicle or the like,as described in Japanese Patent Application Laid-open No. 2004-231011(patent document 1), there is a structure in which a motor-drivensteering assist apparatus is interposed between an upper steering shaftin a steering wheel side and a lower steering shaft in a tire wheelside. A steering force applied to the steering wheel by a driver isassisted by a torque generated by an electric motor.

In the motor-driven steering assist apparatus in the patent document 1,a single unit body covered by a housing has an input shaft to which theupper steering shaft is connected, and an output shaft to which thelower steering shaft is connected. A torque sensor is provided betweenthe input shaft and the output shaft. An electric motor is driven incorrespondence to a detected torque of the torque sensor. A worm gear iscoupled to a rotary shaft of the electric motor, and a worm wheel iscoupled to the output shaft and engaging with the worm gear built-in.The housing can be attached to a vehicle body frame (a vehicle body sidebracket). When the steering torque is applied to the steering wheel, thesteering torque is applied to a torsion bar coupling the input shaft andthe output shaft via the upper steering shaft, and the input shaft andthe output shaft relatively rotate on the basis of a torsion generatedby the torsion bar. Accordingly, the torque sensor detects the steeringtorque on the basis of a displacement in a rotating direction of theinput shaft and the output shaft, and the electric motor is controlledso as to apply an assist force in correspondence to the steering torqueto the output shaft.

In the motor-driven steering assist apparatus provided in theconventional rough road traveling vehicle, when steering the steeringwheel to the maximum, the upper steering shaft and the input shafttwists the torsion bar, so that the torque sensor carries on detectingthe steering torque. Accordingly, the electric motor is continuouslydriven despite that the output shaft and the lower steering shaft reacha steering stroke end.

Further, in the motor-driven steering assist apparatus provided in theconventional rough road traveling vehicle, if an inverse input iscontinuously input from the tire wheel side due to a rock being caughton the tire wheel during steering the steering wheel to the maximum, thelower steering shaft and the output shaft continues twisting the torsionbar, so that the torque sensor continues to detect the steering torque.Accordingly, the electric motor is continuously driven despite that theoutput shaft and the lower steering shaft reach the steering stroke end,thereby experiencing breakage such as a burnout or the like.

SUMMARY OF THE INVENTION

An object of the present invention is to avoid the electric motor frombeing driven to no purpose in a state in which the steering wheel issteered to the maximum, in the motor-driven steering assist apparatus.

Further, an object of the present invention is to avoid the electricmotor from being driven to no purpose even if the inverse input isapplied from the tire wheel side in a state in which the steering wheelis steered to the maximum, in the motor-driven steering assistapparatus.

The present invention relates to a support structure of a motor-drivensteering assist apparatus interposed between an upper steering shaft ina steering wheel side and a lower steering shaft in a tire wheel side. Asteering angle regulating means for limiting a maximum steering angle ofthe upper steering shaft is provided between the upper steering shaftand the vehicle body side.

The present invention relates to a support structure of a motor-drivensteering assist apparatus interposed between an upper steering shaft ina steering wheel side and a lower steering shaft in a tire wheel side. Asteering angle regulating means for limiting a maximum steering angle ofthe lower steering shaft is provided between the lower steering shaftand the vehicle body side.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the detaileddescription given below and from the accompanying drawings which shouldnot be taken to be a limitation on the invention, but are forexplanation and understanding only.

The drawings:

FIG. 1 is a schematic view showing a support structure of a motor-drivensteering assist apparatus;

FIG. 2 is a cross sectional view along a line II-II in FIG. 1;

FIG. 3 is a cross sectional view along a line III-III in FIG. 1;

FIG. 4 is a cross sectional view showing a steering angle regulatingmeans of an upper steering shaft along a line IV-IV in FIG. 1; and

FIG. 5 is a cross sectional view showing a steering angle regulatingmeans of a lower steering shaft along a line V-V in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A motor-driven steering assist apparatus 10 is applied to a rough roadtraveling vehicle, for example, a buggy vehicle, a snowmobile or thelike. The apparatus is interposed between an upper steering shaft 1 in asteering wheel side and a lower steering shaft 2 in a tire wheel side,and assists a steering force applied to the steering wheel by a driveron the basis of torque generated by an electric motor 24.

The motor-driven steering assist apparatus 10 rotatably supports theupper steering shaft 1 to an upper vehicle body side stay 3 via abearing by a support member 4, and a steering wheel attaching member 5is fixed to an upper end portion thereof. The lower steering shaft 2 isrotatably supported to a lower vehicle body side stay 6 via a bearing bya support member 7, and a pitman arm 8 is fixed to an intermediateportion thereof. The pitman arm 8 is coupled to a front tire wheel viaright and left tie rods. The upper vehicle body side stay 3 and thelower vehicle body side stay 6 are supported to a vehicle body frame.

The motor-driven steering assist apparatus 10 has a single unit body 10Acovered by first housing 11 (upper housing or upper cover), secondhousing (main housing), and third housing (lower housing or lower cover)13, as shown in FIGS. 1 to 3. The unit body 10A has an input shaft 21,an output shaft 22, a torque sensor 23, an electric motor 24, a wormgear 25 and a worm wheel 26 built-in.

The motor-driven steering assist apparatus 10 is structured such that anupper end portion of the input shaft 21 to which the upper steeringshaft 1 is connected by a connecting device 1A is supported to the firsthousing 11 (FIG. 2) by the bearing 31. Upper and lower end portions ofthe output shaft 22 to which the lower steering shaft 2 is connected bya connecting device 2A are supported to the second housing 12 and thethird housing 13 by upper and lower bearings 32A and 32B (FIG. 2). Theinput shaft 21 is provided with a serration 21A for connected to theconnecting device 1A in an upper end outer peripheral portion. Theoutput shaft 22 is provided with a serration 22A for connecting to theconnecting device 2A in a lower end outer peripheral portion. A torsionbar 27 is inserted to a hollow portion of the input shaft 21. One end ofthe torsion bar 27 is coupled to the input shaft 21 by a coupling pin27A, and the other end of the torsion bar 27 is inserted to a hollowportion of the output shaft 22 so as to be connected by serration.

When steering torque is applied to the steering wheel, the steeringtorque is also applied to a torsion bar 27 coupling the input shaft 21and the output shaft 22 via the upper steering shaft 1. The input shaft21 and the output shaft 22 are relatively rotated on the basis of atorsion generated by the torsion bar 27. Accordingly, the torque sensor23 detects the steering torque on the basis of displacement in arotating direction of the input shaft 21 and the output shaft 22, andthe electric motor 24 is controlled so as to apply an assist force incorrespondence to the steering torque to the output shaft 22.

A torque sensor 23 is provided with two detecting coils 23A and 23Bsurrounding a cylindrical core 23C engaged with the input shaft 21 andthe output shaft 22, in the first housing 11, as shown in FIG. 2. Thecore 23C is provided with a vertical groove 23E engaging with a guidepin 23D of the output shaft 22 so as to be movable only in an axialdirection, and is provided with a spiral groove 23G engaging with aslider pin 23F of the input shaft 21. Accordingly, when a steeringtorque applied to the steering wheel is applied to the input shaft 21,and a relative displacement in a rotation direction is generated betweenthe input shaft 21 and the output shaft 22 on the basis of an elastictorsional deformation of the torsion bar 27, the displacement in therotation direction of the input shaft 21 and the output shaft 22displaces the core 23C in an axial direction. An inductance of thedetecting coils 23A and 23B caused by a magnetic change around thedetecting coils 23A and 23B due to the displacement of the core 23C ischanged. In other words, when the core 23C moves close to the inputshaft 21, the inductance of the detecting coil 23A to which the core 23Cmoves close is increased, and the inductance of the detecting coil 23Bfrom which the core 23C moves apart is reduced, whereby it is possibleto detect the steering torque on the basis of the change of theinductance.

The electric motor 24 is attached and supported to the second housing 12by a mounting bolt 28, and is driven by a controller (not shown) incorrespondence to the detected torque of the torque sensor 23.

A worm gear 25 is coupled to a rotation shaft 24A of the electric motor24 by a joint 24B, and the worm wheel 26 engaging with the worm gear 25is fixed to the output shaft 22. The worm gear 25 is supported at bothends to the second housing 12 by right and left bearings 41 and 42, asshown in FIG. 3. The worm wheel 26 is fixed to the output shaft 22 justbelow an upper bearing 32A in the output shaft 22, in an inner portionof the second housing 12.

In this case, the joint 24B coupling the rotation shaft 24A of theelectric motor 24 and the worm gear 25 is structured such that a torquelimiter 24C constituted by an elastic ring is interposed in a fittinggap between both the elements (FIG. 3). The torque limiter 24C keepscoupling the rotation shaft 24A and the joint 24B under normal usingtorque conditions of the motor-driven steering assist apparatus 10,allows them to slip under abnormal torque conditions, and does nottransmit the torque of the electric motor 24 to a side of the joint 24B.

Accordingly, in the motor-driven steering assist apparatus, an integralunit body 10A is structured by supporting the upper end portion of theinput shaft 21 and the torque sensor 23 to the first housing 11. Theupper end portion of the output shaft 22, the electric motor 24, theworm gear 25 and the worm wheel 26 are supported by the second housing12. The lower end portion of the output shaft 22 is supported by thethird housing 13. The first housing 11 and the second housing 12 arecoupled by the mounting bolt 14, and the second housing 12 and the thirdhousing 13 are coupled by the mounting bolt 15 (FIG. 2). An oil seal 33is attached in a sealing manner to an upper opening portion of thebearing 31 in the first housing 11, and an oil seal 34 is attached in asealing manner to a lower opening portion of the bearing 32B in thethird housing 13 (FIG. 2).

Further, the motor-driven steering assist apparatus 10 is structuredsuch that the second housing 12 can be attached to the vehicle bodyside. The motor-driven steering assist apparatus 10 is structured, asshown in FIGS. 1 and 2, such that elastic members 51 and 52 such as arubber bush or the like are provided in both sides of attaching bosses12A provided at a plurality of positions, for example, three positions,in a peripheral direction of an outer periphery of the second housing12. The attaching bosses 12A are pinched between upper and lower supportpieces 18A and 18B of forked support portions 18 provided at a pluralityof positions corresponding to the attaching bosses 12A of the vehiclebody side attaching bracket 17 via the elastic members 51 and 52. Theattaching boss 12A is pinched in a floating fixed state between theupper and lower support pieces 18A and 18B via the elastic members 51and 52 by an attaching bolt 16 (a nut 16A) inserted and attached to abolt hole provided in each of he support pieces 18A and 18B of theforked support portion 18, the elastic members 51 and 52, and theattaching bosses 12A. The vehicle body side bracket 17 is supported tothe vehicle body frame.

Accordingly, in the motor-driven steering assist apparatus 10, there areprovided with (A) a first steering angle regulating means 100 forpreventing the electric motor 24 from being driven for no purpose whenthe steering wheel is steered to the maximum, and (B) a second steeringangle regulating means 200 for preventing the electric motor 24 frombeing driven to no purpose even if the inverse input is applied from thetire wheel side when the steering wheel is steered to the maximum, asdescribed below.

(A) First Steering Angle Regulating Means 100 (FIGS. 1 and 4)

The first steering angle regulating means 100 is provided between theupper steering shaft 1 and the vehicle body side, and limits the maximumsteering angle of the upper steering shaft 1.

The first steering angle regulating means 100 is structured, as shown inFIGS. 1 and 4, such that both left and right side portions of an openportion 4B obtained by partially notching an annular wall 4A of anannular support member 4 provided in the upper vehicle body side stay 3are formed as left and right stopper portions 101A and 101B. Aprotruding portion provided in a portion pinched between the left andright stopper portions 101A and 101B of the opening portion 4B in theouter periphery of the upper steering shaft 1 is formed as a stoppedportion 102. The opening portion 4B is provided so as to normally face afront face or a back face facing to, for example, a front side of thevehicle of the annular wall 4A. In the case that the steering wheel isat a neutral position, the stopped portion 102 of the upper steeringshaft 1 exists in a center in the rotating direction with respect to theleft and right stopper portions 101A and 101B of the support member 4. Aleft steering angle θ1 exists between the stopped portion 102 and thestopper portion 101A, and a right steering angle θ2 exists between thestopped portion 102 and the stopper portion 101B (θ1=θ2). When thesteering wheel and the input shaft 1 reach left or right maximumsteering angles θ1M or θ2M (θ1M=θ2M), the stopped portion 102 of theupper steering shaft 1 is brought into contact with the left or rightstopper portions 101A or 101B of the support member 4 so as to bebraked. A relation θ1M=θ1 and θ2M=θ2 is established.

In accordance with the present embodiment, the following operations andeffects can be obtained.

(a) When the steering wheel is steered to the maximum, the maximumsteering angle of the upper steering shaft 1 to which the steering wheelis coupled is limited by the first steering angle regulating means 100.Accordingly, in the maximum steering state, the upper steering shaft 1and the input shaft 21 do not continue twisting the torsion bar 27, andthe torque sensor 23 does not continue detecting the steering torque.The electric motor 24 does not carry on driving for no purpose after theoutput shaft 22 and the lower steering shaft 2 reach the steering strokeend.

(b) It is possible to easily structure the first steering angleregulating means 100 by the stopper portions 101A and 101B in thevehicle body side, and the stopped portion 102 of the upper steeringshaft 1.

(B) Second Steering Angle Regulating Means 200 (FIGS. 1 and 5)

The second steering angle regulating means 200 is provided between thelower steering shaft 2 and the vehicle body side, and limits the maximumsteering angle of the lower steering shaft 2.

The second steering angle regulating means 200 is structured, as shownin FIGS. 1 and 5, such that left and right stopper portions 201A and201B are provided in the vehicle body side stay 6 in a front face, or aback face, facing to, for example, the front side of the vehicle of thesupport member 7, when setting the support member 7 to the lower vehiclebody side stay 6. A V-shaped stopped portion 202 is provided in aportion pinched between the left and right stopper portions 201A and201B in the outer periphery of the lower steering shaft 2. The stoppedportion 202 has plate-like pieces 202A and 202B which are formed in a Vshape by being welded or otherwise fixed to two left and right positionsin the outer periphery of the lower steering shaft 2.

In the case that the steering wheel is at a neutral position, thestopped portion 202 of the lower steering shaft 2 exists in a center inthe rotating direction with respect to the left and right stopperportions 201A and 201B of the vehicle body side stay 6. A left steeringangle θ1A exists between the stopped portion 202 and the stopper portion201A, and a right steering angle θ2A exists between the stopped portion202 and the stopper portion 201B (θ1A=θ2A). When the lower steeringshaft 2 reaches maximum steering angles θ1M or θ2M (θ1M=θ2M) togetherwith the upper steering shaft 1 on the basis of forces applied to thesteering wheel and the input shaft 1, the stopped portion 202 of thelower steering shaft 2 is close to or brought into contact with the leftor right stopper portions 201A or 201B of the vehicle body side stay 6so as to be braked. A relation θ1M=θ1A and θ2M=θ2A is established.

In this case, in accordance with the present embodiment, since the firststeering angle regulating means 100 in the side of the upper steeringshaft 1 is provided in parallel to the second steering angel regulatingmeans 200 in the side of the lower steering shaft 2, it is preferable tofirst bring the stopped portion 102 of the first steering angleregulating means 100 into contact with the stopper portion 101A or 101Band next bring the stopped portion 202 of the second steering angelregulating means 200 into contact with the stopper portion 201A or 201B(θ1<θ1A, θ2<θ2A), when rotating the steering wheel and the input shaft 1to the maximum steering angle position and setting the lower steeringshaft 2 to the maximum steering angle position by extension.

In accordance with the present embodiment, the following operations andeffects can be obtained.

(a) If the inverse input is applied from the tire wheel side when thesteering wheel is steered to the maximum, the second steering angleregulating means 200 limits the maximum steering angle of the lowersteering shaft 2. Accordingly, in the maximum steering state, the lowersteering shaft 2 and the input shaft 22 do not continue twisting thetorsion bar 27, and the torque sensor 23 does not continue detecting thesteering torque. The electric motor 24 does not continue driving for nopurpose after the output shaft 22 and the lower steering shaft 2 reachthe steering stroke end.

(b) It is possible to easily structure the second steering angleregulating means 200 by the stopper portions 201A and 201B in thevehicle body side, and the stopped portion 202 of the lower steeringshaft 2.

As heretofore explained, embodiments of the present invention have beendescribed in detail with reference to the drawings. However, thespecific configurations of the present invention are not limited to theillustrated embodiments but those having a modification of the designwithin the range of the presently claimed invention are also included inthe present invention. In the present invention, the gear traintransmitting the rotation of the electric motor to the output shaft isnot limited to the structure constituted by the worm gear and the wormwheel.

Although the invention has been illustrated and described with respectto several exemplary embodiments thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions and additions may be made to the present invention withoutdeparting from the spirit and scope thereof. Therefore, the presentinvention should not be understood as limited to the specific embodimentset out above, but should be understood to include all possibleembodiments which can be encompassed within a scope of equivalentsthereof with respect to the features set out in the appended claims.

1. A support structure of a motor-driven steering assist apparatusinterposed between an upper steering shaft in a steering wheel side anda lower steering shaft in a tire wheel side, wherein a steering angleregulator for limiting a maximum steering angle of the upper steeringshaft is provided between the upper steering shaft and the vehicle bodyside, the steering angle regulator is constituted by a stopper portionprovided in the vehicle body side and a stopped portion provided in theupper steering shaft, and the stopped portion of the upper steeringshaft is braked by the stopper portion in the vehicle body side at atime when the upper steering shaft reaches the maximum steering angle,the motor-driven steering assist apparatus rotatably supports the uppersteering shaft to an upper vehicle body side via a bearing by a supportmember, the support member is formed in an annular shape having anopening portion obtained by partly notching an annular wall in aperipheral direction, and both right and left side portions in theopening portion of the annular wall in the annular support member areformed as the right and left stopper portions, and a protruding portionprovided in a pinched between the right and left stopper portions of theopening portion in an outer periphery of the upper steering shaft isformed as the stopped portion.
 2. A support structure of a motor-drivensteering assist apparatus as claimed in claim 1, wherein the openingportion is provided so as to normally face to a front face or a backface facing to a front side of the vehicle of the annular wall, and thestopped portion of the upper steering shaft exists at a center in arotating direction of the support member with respect to the right andleft stopper portions, at a time when the steering wheel exists at aneutral position.
 3. A support structure of a motor-driven steeringassist apparatus interposed between an upper steering shaft in asteering wheel side and a lower steering shaft in a tire wheel side,wherein a steering angle regulator for limiting a maximum steering angleof the lower steering shaft is provided between the lower steering shaftand the vehicle body side, wherein the steering angle regulating meansis constituted by per portion provided in the vehicle body side and astopper portion provided in the lower steering shaft, and the stoppedportion of the lower steering shaft is braked by the stopper portion inthe vehicle body side at a time when the lower steering shaft reachesthe maximum steering angle, the lower steering shaft of the motor-drivensteering apparatus is rotatably supported to a lower vehicle body sidestay via a bearing by a support member, the right and left stopperportions are provided in a vehicle body side stay in a front face or aback face facing to the front side of the vehicle of the support member,at a time when the support member is provided in the lower vehicle bodyside stay, and the V-shaped stopped portion is provided in a portionpinched between the right and left stopper portions in an outerperiphery of the lower steering shaft.
 4. A support structure of amotor-driven steering assist apparatus as claimed in claim 3, whereinthe stopped portion is constituted by a plate-like piece formed in a Vshape with each other by being welded to two right and left positions ofthe lower steering shaft.